The Surprising Truth About What Marriage Does to Your Body

A new study suggests people in committed relationships may have higher body weights.

Does coupling up make you pack on the pounds? While some recent studies tout real health benefits of marriage, new data based on 10,226 respondents in nine European countries suggests the institution might actually cause your waistline to expand.

The study, conducted by a team of researchers from Universität Basel in Switzerland and published in the journal Social Science and Medicine, compared the body mass index (BMI)—or weight-to-height ratio—of married couples with that of singles. In all countries, their findings show that married men and women generally eat better than singles, but weigh significantly more and exercise less.

In the study, single men had an average BMI of 25.7, while married men averaged at 26.3. There was less of a disparity between women: The average BMI was 25.1 for singles and 25.6 for married women. According to the World Health Organization, a normal body mass index is between 18.5 and 24.99. Those classified as overweight have a BMI between 25 and 29.99—a number above 30 indicates obesity.

"Our findings show how social factors can impact health. In this case, that the institution of marriage and certain changes in behavior within that context are directly related to nutrition and body weight," Ralph Hertwig, director of the Center for Adaptive Rationality at the Max Planck Institute for Human Development in Berlin, said in a statement.

Though married people reported eating less convenience foods and more unprocessed products, they also admit to exercising less, which may account for the higher BMI amongst those in committed relationships. “Our findings indicate that couples are not healthier in every respect, as has previously been assumed," Jutta Mata, lead author of the study and Assistant Professor of Health Psychology at the University of Basel, said in the statement.